1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter, referred to as "LCD") panel, and more particularly to a liquid crystal display device structure constructed to prevent an LCD device provided therein from being damaged due to moisture penetration.
2. Description of the Prior Art
FIG. 1 is a schematic cross-sectional view showing the construction of a prior art TFT-LCD module.
As shown in FIGS. 1 and 2, the prior art TFT-LCD module comprises a TFT-LCD (thin film transistor-liquid crystal display) panel 10, a PCB (printed circuit board) substrate 20, a bare chip 31 of a driving IC (integrated circuit) for driving the TFT-LCD panel 10 and a TCP (tape carrier package) 30 having both surfaces on which the PCB substrate 20 and the TFT-LCD panel 10 are attached.
The TFT-LCD panel 10, as shown in FIGS. 2A to 2C, broadly comprises a display part 11 and a pad part 14. The display part 11 has a TFT (thin film transistor) array portion formed on a lower substrate 12 (FIGS. 2b and 2c) and a pixel portion formed on an upper substrate 13. The pad part 14 has a gate pad portion 14-2 formed at a left side of the display part 11, for sequentially supplying a driving voltage to gate bus lines of the TFT array portion, and a source pad portion 14-1 for supplying a data voltage to a liquid crystal cell. A passivation layer 17 is deposited only on the display part 11 of the TFT-LCD panel 10, and not on the pad part 14.
Also, the TFT-LCD panel 10 has the upper substrate 13 and the lower substrate 12 spaced from each other and a liquid crystal layer 15 is provided therebetween by liquid crystal injection and sealing. Polarization plates 16-1 and 16-2 are attached to outside surfaces of the substrates 12 and 13. It is shown in FIG. 2 that the gate pad portion 14-2 of the pad portion 14 is located adjacent a left side of the display part 11. However, the gate pad portion 14-2 may also be located adjacent a right side of the display part 11.
The method for fabricating the above-described TFT-LCD module will be described below:
First, a TFT array portion and the pad part 14 are formed on a lower substrate 12. Then, a color filter constituting a pixel portion is formed on the upper substrate 13. The upper and lower substrates 13 and 12 are spaced from each other and a liquid crystal layer 15 is formed therebetween. Also, polarization plates 16-1 and 16-2 are respectively attached to outside surfaces of the substrates 12 and 13. Next, after formation of a TCP 30 provided with a bare chip 31 for driving a TFT-LCD panel 10, inner leads of the TCP 30 are bonded to the pad part 14. Finally, the TFT-LCD panel 10 and the TCP 30 are assembled on a PCB substrate 20.
FIG. 3 shows a schematic view showing the construction of another prior art TFT-LCD panel, wherein FIG. 3A is a plane view thereof and FIG. 3B is a cross-sectional view thereof. Component elements having similar functions to the component elements of the TFT-LCD panel shown in FIGS. 1 and 2, and are indicated by the same reference numerals, therefore descriptions thereof are omitted.
Referring to FIGS. 3A and 3B, a gate pad portion 14-2 of a pad part 14 is established at a left side of a display part 11 in the TFT-LCD panel 10 and provided with a plurality of pads 2a. Source pad portions 14-1 of the pad part 14 are established at upper and lower sides of the display part 11. Each source pad portion 14-1 is provided with a plurality of pads 1a. The number of the pads 2a in the gate pad portion 14-2 is equal to the number of gate bus lines. The number of the pads 1a in the source pad portion 14-1 is equal to the number of source bus lines.
FIG. 4 is a plane view of the TCP 30 of FIG. 1 connected with the pad part 14 in the TFT-LCD panel 10, shown in FIG. 1. The TCP 30 has a mounting portion 32 where the bare chip 31 (see FIG. 1) of the driving IC is mounted, inner leads 33 connected to respective pads of the pad part 14 (see FIG. 2), and slanting leads 34 for electrically connecting the bare chip 31 with the inner leads 33.
The number of the inner leads 33 is equal to the number of the pads. The inner leads 33 are indicated in FIG. 4 by thin lines but in practice, inner leads 33 have a specified width wide enough to be connected with the respective pads. The respective pads are electrically contacted with the inner leads 33 during bonding of the liquid crystal module.
Subsequently, during assembly of the liquid crystal module, the TFT-LCD panel is adhered to the TFT-LCD module, thereby allowing input data to be displayed on the display part 11 by an electric field occurring due to a voltage applied through each of the pads.
In the prior art TFT-LCD panel of FIGS. 1-3, the passivation layer 17 is not formed over the whole surface of the TFT-LCD panel, but is formed only on the display part 11, the pads of the pad part 14, all which are connected to inner leads of the TCP 30, are exposed. Since the pad part 14 is exposed, moisture can penetrate to the pad part 14 and damage the pad part 14.
To prevent damage to the pad part 14 caused by moisture penetration, a silicon epoxy is deposited between a glass substrate and an edge portion of a pad where a TCP is bonded. However, since a pin-hole is generated in such a silicon epoxy, it is impossible to avoid damage of the pad part caused due to moisture penetration through the pin-hole.
When the above situation happens, an electrical open of a bus line on the display part occurs therein due to a damage of the pad part, and a TFT-LCD device of a TFT-LCD panel is seriously affected.